Third rail insulator



FIG. 1 is a top plan view of a third rail insulator;

FIG. 2 is a front elevational view thereof, the rear elevational view being a mirror image thereof;

FIG. 3 is a right-side elevational view thereof, the left-side elevational view being a mirror image thereof;

FIG. 4 is an isometric view thereof; and,

FIG. 5 is an isometric view thereof, showing the design with a third rail mounted thereto.

The broken lines represent environmental structure and form no part of the claimed design. 

CLAIM The ornamental design for a third rail insulator, as shown and described. 